The conventional brake assembly for bicycles generally include drum brake assembly, cantilever brake assembly, V-type brake assembly and hydraulic disk brake assembly. All of the conventional brake assemblies are designed for the safety of the cyclists and the latest hydraulic disk brake assembly comprises a brake part fixed to the bicycle frame and a hydraulic operation unit is connected to the brake part so as to drive a piston of a cylinder. A brake lever is pivotably connected to the handlebar of the bicycle and the hydraulic oil is delivered to the piston by operation of the brake lever. The hydraulic oil drives a clamp to clamp the brake disk which is fixed to the axle of the wheel so that the wheel is stopped. There is only one set of the piston to be used to drive the clamp to brake the wheel.
A conventional hydraulic brake lever assembly known to applicant comprises a tubular frame with a narrowed open end and a lever is pivotably connected to one side of the open end of the frame. The frame is connected to the handlebar by the other side of the open end. A hydraulic pump unit has a piston received therein and a threaded section is formed at a narrowed end of the hydraulic pump unit. The threaded section is inserted through the frame and connected to a hydraulic oil pipe. The brake lever has a base portion that has a push rod which has an enlarged head inserted in the open end of the hydraulic pump unit. By operation of the brake lever, the piston is moved to drive the hydraulic brake assembly. The hydraulic pump unit is located in the frame so as to avoid the dust and water from entering the hydraulic pump unit. The parts of the hydraulic brake lever assembly can be easily replaced so that the cost of the maintenance is low.
However, the single hydraulic pump unit provides only one travel for the piston so that the gap between the lining plates and the brake disk has to be small enough such as 0.3 mm, to allow the lining plates to contact the brake disk as soon as possible to shorten the braking time required. However, because the gap is so small so that the brake disk contacts the lining plates during riding when the brake disk is deformed after a period of time of use. Therefore, both of the lining plates and the brake disk are worn. Furthermore, pebbles can be easily stocked in the small gap and wear the brake disk and the lining plates. The gap may also be changed when the frame, the hub, the front fork are not precisely installed.
The present invention intends to provide a brake lever assembly which includes two cylinder units to improve the shortcomings of the conventional brake assemblies.